Discovery of a new great ape: The Tapanuli orangutan

An international team of researchers*, including Professor Serge Wich from Liverpool John Moores University, have just described¹ a new great ape species, the Tapanuli orangutan (Pongo tapanuliensis), found in upland forests in North Sumatra in Indonesia. With no more than 800 individuals, this species is the most endangered great ape species.

The scientists described the new species in Current Biology, based on morphological and extensive genomic evidence. The new orangutan species, Pongo tapanuliensis, or Tapanuli orangutan, is endemic to the three Tapanuli districts of North Sumatra, Indonesia and occurs in roughly 1,100 km² of upland forest in the Batang Toru Ecosystem.

A recent independent study² by Indonesian and international scientists, led by the study’s co-author Professor Serge Wich, indicated that no more than 800 individuals remain in the Batang Toru Ecosystem. Conservationists have drawn attention to the fact that urgent action is required to carefully review current proposals for further developments in the area that would threaten the livelihood of the new species.

There is strong anthropogenic pressure on the Tapanuli orangutan due to conversion of pristine forest for mining, plans to build a hydro-electric dam, and general human encroachment.

Professor Serge Wich, who is based at the LJMU School of Natural Sciences and Psychology, has been involved in surveys and research on this new species since 2001 and provided ecological expertise to the study.

He commented: “It is incredibly exciting that a new orangutan species has been described and it’s a wonderful addition to Indonesia's high biodiversity. At the same time the low number of Tapanuli orangutans in the wild indicates that there can be no complacency in terms of its conservation. If steps are not taken quickly to reduce current and future threats to conserve every last remaining bit of forest, we may see the discovery and extinction of a great ape species within our lifetime.”

This is an amazing discovery," said head of UN Environment, Erik Solheim. "It is essential that we do everything in our power to protect the tiny numbers of this new species."

Professor Serge Wich, who is the chair of the scientific commission of the Great Apes Survival Partnership (GRASP), also contributed to the GRASP study ³ on sustainable forest management in Sumatra, which looked into sustainable pathways to development while keeping this important orangutan habitat intact: “If steps are not taken quickly to reduce threats to the small orangutan habitat in Batang Toru,” GRASP coordinator Dr. Johannes Refisch points out, “we may see the newly discovered species going extinct very soon." 

Footage of a baby Tapanuli orangutan being fed. They feed on several food items that no other orangutans in other populations do and their long calls (the loud booming call that a flanged male orangutan makes) are also different from other populations.

The steps taken to find the new apes species

“Despite nearly 50 years of orangutan research in Sumatra, the Batang Toru population was only ‘rediscovered’ in 1997, during a series of field surveys” says Professor Erik Meijaard, who carried out the initial survey south of Lake Toba looking for orangutan populations. In 2005, the Sumatran Orangutan Conservation Programme (SOCP) and other non-governmental organizations intensified previous research and conservation efforts on the orangutans in the Batang Toru Ecosystem, together with several universities, and Indonesian authorities. As a part of this effort, a research station was established in 2006 by SOCP, allowing for a more detailed look at their behavioural ecology and genetics.

It was not until 2013, however, when skeletal material from an adult male orangutan killed in a human-animal conflict became available, that SOCP’s Matthew Nowak and colleagues realized the uniqueness of the Batang Toru population. “We compared this skull to other orangutan skulls.” states Anton Nurcahyo, an Indonesian PhD student from the Australian National University. “We were completely surprised to find that the skull is quite different in some characteristics from orangutan skulls we had seen before”. While this suggested that the Batang Toru population was potentially unique, much stronger evidence was required to actually determine whether the Batang Toru orangutans were indeed a different species. This was achieved by the largest genomic study of wild orangutans to date which has been made possible by decades of data collection at most of the field sites where orangutans are studied.

“For quite some time, we had been working on genomic data to investigate the genetic structure and evolutionary history of all existing orangutan populations” say Drs Maja Mattle-Greminger and Alexander Nater, responsible for the genomic analyses at the University of Zurich. “One consistent result was that we identified three very old evolutionary lineages among all orangutans, despite only having two species currently described”.

“When we realized that Batang Toru orangutans are morphologically different from all other orangutans, the pieces of the puzzle fell into place” adds Prof. Michael Krützen from the University of Zurich and responsible for the study. “The oldest evolutionary line in the genus Pongo is actually found in Batang Toru orangutans, which appear to be direct descendants of the first Sumatran population in the Sunda archipelago.”

Extensive computer modelling carried out by Dr Nater, aimed at reconstructing the population history of orangutans, revealed that the Batang Toru population appears to have been isolated from all other Sumatran populations for at least 10-20’000 years, after which the low levels of influx of males from the northern populations had ceased. Adding additional evidence based on behavioral observations and ecological surveys from Batang Toru and other sites provided further support for the morphological and genetic findings.

*Professor Serge Wich worked alongside Professor Dr. Michael Krützen, University of Zurich, Matthew Nowak, Sumatran Orangutan Conservation, Dr Alexander Nater, University of Constance, Dr Maja Mattle-Greminger, University of Zurich, Dr Erik Meijaard, Australian National University and Anton Nurcahyo, the Australian National University for this research

Photos: The Tapanuli orangutan Photo Credits: Maxime Aliaga

Audio: Long calls from a flanged male Tapanuli orangutan (c) James Askew

References:

¹ Nater, A. et al. (2017). Morphometric, behavioral, and genomic evidence for a new orangutan species. Current Biology.

² Wich, S et al. (2016). Land-cover changes predict steep declines for the Sumatran orangutan (Pongo abelii). Science Advances 2(3), e1500789, DOI:

10.1126/sciadv.1500789.

3 Wich et al. (2011): Orangutans and the economy of sustainable forest management in Sumatra. UNEP, PanEco, YEL, ICRAF, GRID-Arendal. ISBN 978-82-7701-095-3.